In the Sahara nation of Niger, four U.S. Green Berets and at least one Nigerien soldier were killed this week, and two American troops were wounded in an ambush. The U.S. military Africa Command says its forces are in Niger training their local counterparts in counterterrorism, intelligence and security techniques.

The region remains menaced by extremist violence with militants linked to al-Qaida and the Islamic State operating in the area. Ofeibea Quist-Arcton monitors the region for NPR. And she reminds us of what happened near the border between Niger and Mali on Wednesday.

OFEIBEA QUIST-ARCTON, BYLINE: The U.S. military Africa Command, AFRICOM, says U.S. and Nigerien troops were on a routine joint patrol in the southwest of Niger near the border in Mali when they came under hostile fire. This is the first time ever that U.S. forces - and President Trump has said 600-plus are in Niger, training - first time U.S. forces have died in Niger.

SIEGEL: Now, U.S. special forces say they're in Niger training the Nigerien army. But if U.S. troops were out on patrol in an area where there are hostile forces, are they in fact in a combat role in Niger?

QUIST-ARCTON: This is the question that many people are asking, Robert. You know, the military - the U.S. military says the troops are playing a train, advise and assist role with its partners like Niger, whether it's in the Sahel or even the Horn of Africa.

But AFRICOM acknowledging that these troops in the southwest of Niger were carrying out this joint patrol with Nigerien forces makes that sort of training and assistance and intelligence-sharing maybe a little unclear about how broadly this assistance is defined. And you have the Sahel watchers saying Wednesday's attack reveals how this training has kind of shifted gear almost into military operations.

SIEGEL: You speak of the Sahel, of the Sub-Saharan region. Give us a sense of this entire region. It isn't only Niger that's facing extremist attacks and violence, is it?

QUIST-ARCTON: It's become hugely unstable. Probably Mali is the country that most people will have heard of in the Sahel. I mean, militants have intensified attacks on U.N. peacekeepers and Malian soldiers and civilians even though they were pushed back, these militants, after occupying northern Mali, including Timbuktu, and then pushed out by a French military intervention in 2003. And so this regional extremist threat continues, Robert.

And the U.S. and other Western powers in their counterterrorism efforts continue to strengthen their presence on the ground, and the extremists seem ready to take them on. Plus, of course, we have the threat of Boko Haram in - across the border in Nigeria spilling over into Niger, Cameroon, Chad and so on. So it's a deeply unstable region. And, of course, Libya not so very far away.

SIEGEL: The Obama administration authorized the U.S. military to begin operating surveillance drones out of central Niger. Has that been effective? Do we know?

QUIST-ARCTON: Well, we're told that for surveillance and so on, they are doing some good work. And a new $100 million base to boost the efforts by the allies in Niger to combat extremism should better protect its porous borders. But you have these attacks every so often that are deadly. And now American troops killed, as I said, Robert, for the first time.